1. Field of the Invention
The invention relates to a linear guide bearing apparatus making use of rolling of balls, and in particular to an improvement of a linear guide bearing apparatus interposing separators between the balls.
2. Description of the Related Art
As a linear guide bearing apparatus of the related art making use of rolling of balls, for example, there is, as shown in FIG. 7, a linear guide apparatus which is furnished with a guide rail 1 elongated in an axial direction and a slider 2 movably crossing thereover. The guide rail 1 is defined at both sides with ball rolling grooves 3 respectively in the axial direction. On the other hand, as shown in FIG. 8 being a cross sectional view, a main body 2A of a slider 2 is defined with ball rolling grooves 6 in opposition to the ball rolling grooves 3 at the inside of both wings 4.
Both opposite ball rolling grooves 3, 6 form a loading ball rolling path A, and balls K of many steel balls roll while supporting load, so that the slider 2 move on the guide rail 1 in the axial direction. Following this moving, the ball K intervened between the guide rail 1 and the slider 2 moves to an end part of the main body 2A of the slider 2, and in order to continuously move the slider in the axial direction, the balls K must be unlimitedly circulated.
Therefore, a linear penetrating hole 7 is formed as a ball returning path axially penetrating in the wings 4 of the slider main body 2A, and at the same time, end caps 5 are equipped at both front and rear ends of the slider main body 2A, where a ball circulating path 8 is formed which is curved in half toroid for communicating the loading ball rolling path A of both ball rolling grooves 3 and 6 with the ball returning path 7, thereby to compose an endless ball circulating path. The ball circulating path 8 is composed of an outside guiding face 8a and an inside guiding face 8b. The outside guiding face 8a is a semi arc groove formed in the inside end of the end cap 5 being an outside guiding member. The inside guiding face 8b is an outer circumference of a half column shaped inside guiding member 9 (also called as return guide) secured to the end face of the slider main body 2A.
Although not shown in FIG. 8, there is also a case that the separator T (also called as retaining piece), as shown in FIG. 9, interposed between the adjacent balls K and K in the unlimited circulating path.
Applicant invented linear guide apparatus of improving operating performance by specifying sizes and shapes of the separator T (Japanese Patent Application No. Hei.11-166900). This is, as shown in FIG. 9, that the separator T is substantially cylindrical at an outer circumference Q and has concave parts W at both sides for contacting the balls K. Under a condition that the balls K are contacted with the concave faces W, an axial line L of the separator coincide with a straight line combining central points O and O of the adjacent balls K and K, and the radius of curvature of the concave face part W contacting with the ball K is almost equal to the radius of the ball K.
The separator T has effects of suppressing zigzag phenomena of the ball to heighten the operating performance and suppressing noises to heighten noise characteristics. The larger the holding margin of the ball, that is, the larger the outer diameter LØ of the separator T, the larger the effects, and a maximum outer diameter size is regulated to be sizes interfering with the inside guiding member 9. FIG. 9 shows a condition where the ball K rolls while contacting with both of the outside guiding face 8a and the inside guiding face 8b of the ball circulating path 8, namely, a condition of “no space and no playing”. The maximum value LØ of the outside dimension of the separator T can be expressed the following formula (1) based on a theorem of three dimensional square.LØ=2{(LR−Da/2)2−(LSP/2)2}1/2−2Lr  (1)herein,                LØ: the maximum outer diameter when the separator T makes no playing        Da: the ball diameter        LSP: span between balls        LR: the radius of the outside guiding face 8a         Lr: the radius of the inside guiding face 8b.         
Under the condition of “no space and no playing” of the balls K with respect to the inner and outer guiding faces 8a, 8b of the ball circulating path 8, since the balls do not always roll smoothly, taking the allowable dimensional precision in production into consideration, it is general to prepare playing of about 10% of the ball diameter between the ball K and the ball rolling circulating path 8, irrespective of presence or absence of the separator T.
FIG. 10 shows a case of a general ball circulating path 8 providing somewhat playing in rolling of the ball K, and the maximum outer diameter size LØmax of the separator T at this time is expressed by the following formula (2), which can be made larger than the maximum outer diameter LØ without preparing the playing.LØmax=2{(LR−Da/2)2−(LSP/2)2}1/2−2(LR−Da−Ld)  (2)herein,                LØmax: the maximum outer diameter of the separator T (a little playing)        LØ: the maximum outer diameter when the separator T makes no playing        Da: the ball diameter        LSP: span between balls        LR: the radius of the outside guiding face 8a         Lr: the radius of the inside guiding face 8b         Ld: the amount of “playing”        
However, the separator T having the maximum outer diameter size LØmax under the condition of “with playing” (FIG. 10) of the linear guide bearing apparatus shown in JP-A-11-166900 is involved with the problem that the outer diameter of the separator T is made as large as possible for heightening the ball holding effect by enlarging a holding margin, but the interference with the slider main body 2A is created so that it is difficult to provide an improving effect of sufficient operating performance. In short, as shown in FIG. 10, it is preferable that a little playing is present between the ball K and the inside guiding member 9 in the ball circulating path 8, but in contrast, the ball K must not have the playing in the loading ball rolling path A. Thus, a corner portion C which is present at an edge in the loading ball rolling path A of the slider main body 2A equipped with the inside guiding member 9 (return guide) in the ball circulating path 8, cannot but inevitably be a little protruded toward the loading ball rolling path A. This protruded corner portion C interferes with the separator T.
The above mentioned patent application showes that it is effective to regulate the maximum outer diameter LØmax of the separator T within the range of 60 to 80% of the ball diameter Da. But, when using the separator T as large as possible which is an outer diameter of about 70 to 80% near to the upper limit, in order to avoid the interference, the inside guiding face 8b of the inside guiding member 9 is made a composite curve comprising a plurality of curves different in centers and radii of curvature, not a simple semicircle, so that the inside guiding member 9 is remarkably complicated in shape, inviting cost-up.
Inventors noticed unsolved problems of the related art, made studies and found that even if the playing becomes larger to a certain degree between the ball and the inside guiding member in the ball circulating path, an effect for heightening the ball holding function by enlarging the outer diameter of the separator T exceeds an influence by the playing, and as a result, the operating performance of the linear guiding apparatus is improved, and have realized this invention.